PREPARATION OF CHARTS Bomg 
9.1 Procedure for Extrapolation of Altitude. 
a. 
b. 
Determine the pressure difference between the terminating 
level and the next higher mandatory level (i.e., 12-10 = 2 mbs). 
Add the pressure value determined in (a) to the pressure of 
the terminating level (i.e., 12+2 = 14 mbs). 
Mark the point on the temperature curve corresponding to the 
value in (b) (i.e., point A, the terminating temperature is point 
B). 
Place a straight edge between the point found in (c) and the 
terminating point (i.e., points A and B). 
With the straight edge aligned with points A and B, extend the 
temperature curve linearly with a dashed line from the ter- 
minating point to the mandatory pressure level (i.e., dashed 
line B-C). 
Note the mean virtual temperature in the stratum (or strata) 
bounded by the standard levels commencing with the standard 
level below the terminating level to the mandatory level above 
the terminating level. For this purpose use the actual temper- 
ature curve up to the terminating point and the extrapolated 
temperature curve from this point to the mandatory level (i.e., 
curve D-B-C). 
Compute the altitude of the mandatory level in the usual way, 
using the thickness tab marks on the adiabatic chart and com- 
mencing with the altitude of the standard level below the ter- 
minating level. 
9.2 Entry of Extrapolated DataonWBAN-31(_ ). Enter the extrapolated 
altitude in the constant pressure data block pertaining to that surface, and 
ericlose the entry in parentheses. Enter ''Extrapolated'' above the con- 
stant pressure data block. 
The pressure altitude curve will not be drawn to the extrapolated height. 
A circled dot, however, will be entered to indicate the altitude and will 
be used as a check on the accuracy of the calculations. 
Laks (oy) 
FMH#3 
